This invention relates to input input scanners and, more particularly, to methods and means for achieving high resolution raster input scanning through the use of low resolution, two dimensional image sensors, such as integrated charge coupled device (CCD) area arrays.
Others have already recognized that charge coupled devices (CCD's) may be advantageously utilized as photosensitive detector elements for raster input scanners. It has been shown that many mutually independent CCD's can be formed on a single chip of semiconductive material, such as silicon. Nevertheless, the chip lengths and the CCD detector densities which can be obtained using state of the art semiconductor fabrication techniques are still not sufficient to permit the manufacture of an integrated linear CCD detector array having the high line scanning resolution capability demanded of some raster input scanners.
In view of that limitation, some thought has been given to the seemingly simple expedient of stringing a plurality of linear integrated CCD arrays together to form a longer, composite linear detector array. However, it has been found that it is difficult to achieve and maintain the alignment of the individual integrated arrays that is essential to the linearity of the composite array. Another suggestion which has been made for applying integrated CCD detector arrays to high resolution raster input scanning involves optically interlacing or stitching the detector elements within several rows of a two dimensional integrated array to perform the scanning. See, for example, U.S. Pat. No. 4,080,633 of Gary K. Starkweather, which issued Mar. 21, 1978 to the assignee of this application. That is an effective approach, but it suffers from the disadvantage of requiring relatively complex and difficult to align optics for imaging the subject which is to be scanned onto the detector array.